1. Field of the Invention
The present invention relates generally to the design and use of medical devices, and more particularly to a method and system for establishing temporary access to a patient's vascular system for hemodialysis and other extracorporeal blood treatments.
Access to a patient's vascular system can be established by a variety of temporary and permanently implanted devices. Most simply, temporary access can be provided by the direct percutaneous introduction of a needle through the patient's skin and into a blood vessel. While such a direct approach is relatively simple and suitable for applications which are limited in time, such as intravenous feeding, intravenous drug delivery, and the like, they are not suitable for hemodialysis and other extracorporeal procedures that must be repeated periodically, often for the lifetime of the patient.
For hemodialysis and other extracorporeal treatment regimens, a variety of transcutaneous catheters and implantable ports have been proposed over the years. Transcutaneous catheters, such as the Tesio catheter available from Med Comp and the Perm-Cath.TM. available from Quinton, comprise a single catheter tube having a distal end placed in a vein in an in-dwelling manner and a proximal end which extends through the skin and is which available for connection to a hemodialysis or other blood treatment system. Such catheter includes a DACRON.RTM. cuff disposed just beneath the skin in order to reduce the risk of infection.
Implantable ports, in contrast, are entirely subcutaneous and connected to a vein or an artery by a subcutaneous cannula. Access to the port is achieved by percutaneous placement of a needle or other connecting tube. Such ports typically comprise a needle-penetrable septum to permit percutaneous penetration of the needle. Recently, several valved-port designs have been proposed, where introduction of a needle or other access tube opens the valve to provide flow to the cannula which connects to the blood vessel.
Both the transcutaneous and implanted port vascular access systems suffer from certain disadvantages and limitations. For example, both such access systems permit only limited blood flow rates. In the case of transcutaneous catheters, the limited flow rates result from the generally small lumen diameters available in in-dwelling venous catheters. In the case of implanted port access systems, the limited flow rates have resulted from both the port structures and the relatively small lumen diameters available in the cannulas which connect the port to the blood vessel. Such limited blood flow rates are problematic since they prolong the duration of the associated extracorporeal blood treatment protocol, such as hemodialysis, hemofiltration, and apheresis.
The initial implantation of both the transcutaneous and implanted port vascular access systems has also been problematic. Such systems generally comprise a single catheter or cannula which is connected to or implanted within the blood vessel and brought to the external attachment point, i.e. either the implanted port or transcutaneous tract through the skin. The subcutaneous placement of the catheter or cannula is difficult in a number of respects. For example, catheters and cannulas having their distal ends implanted in the jugular vein are typically bent by an angle from 90.degree. to 180.degree. to locate their associated ports or catheter exit points at an appropriate location on the patient's chest. Such bends also can accommodate excess length in the connecting catheters and cannulas. The bends, however, are also subject to kinking and other problems. Thus, it would be desirable to provide methods and systems for implanting vascular access catheters and cannulas which can accommodate different patient characteristics and placement patterns.
An even more significant problem with prior transcutaneous and implanted port vascular access systems has been replacement. It is often necessary to replace a transcutaneous catheter when its distal end becomes dysfunctional due to plugging or other causes. Heretofore, it has usually been necessary to remove the entire catheter, including the subcutaneous cuff which has become ingrown in the tissue. In the case of implanted port systems, either the port or the cannula attached to the blood vessel could become dysfunctional. Heretofore, it has generally been necessary to remove both the port and the implanted cannula when either needs to be replaced. It would therefore be desirable to provide improved methods and systems which permit only a portion of the implanted system to be replaced when other portions of the system remain functional.
For these reasons it would be desirable to provide improved transcutaneous and implanted port access systems and methods for their implantation and replacement which would overcome at least some of the problems described above. In particular, it would be desirable if the vascular access systems could provide enhanced flow rates, preferably above at least 200 ml/minute, more preferably above 500 ml/minute, still more preferably above 600 ml/minute, and even more preferably above 700 ml/minute. Systems and methods of the present invention should also facilitate both initial implantation and, if necessary, subsequent replacement of system components with minimum trauma to the patient. At least some of these objectives will be met by the different aspects of the present application described below.
2. Description of the Background Art
U.S. Pat. Nos. 5,562,617 and 5,041,098 are exemplary of implantable systems employing cannulas extending between a port and a blood vessel for providing extracorporeal circulation. U.S. Pat. Nos. 5,417,656 and 5,281,199 show implantable ports which are connected to vascular cannulas via a transition region (FIG. 1A) and to a multiple branch cannula (FIG. 21). U.S. Patent No. 4,892,518 shows an implanted port with a transition region extending to a cannula. U.S. Pat. Nos. 5,234,406 and 5,215,530 show two-piece catheters having a distal portion which can be placed percutaneously. The '406 patent discloses a large diameter proximal portion to enhance the flow rate of anesthetics to the subarachnoid region of the spine. U.S. Pat. Nos. 5,203,771 and 4,181,132 show implantable connectors which provide for percutaneous access to implanted shunts.
Related co-pending applications, assigned to the assignee of the present application, include Ser. Nos. 08/745,903; 08/724,948; 08/634,634; 08/539,105; and 60/036,124.
The full disclosures of each of the U.S. Patents and co-pending applications listed above are hereby incorporated herein by reference.